Patent GB-515475-A (GB)
Title: Improvements in or relating to television pulse generating systems and the like
IPC: H04N5/06
Filed: 1938-05-04
Abstract: 515,475. Television. BEATTY, W. A. May 4, 1938, No. 13259. [Classes 40 (iii) and 40 (v)] In a pulse generating system, particularly for producing synchronizing impulses for television, pulses are selected at a submultiple frequency from a train of short pulses by means of an electronic device (e.g. a cathode-ray tube or thermionic valve) the output of which is initiated upon the arrival of each nth pulse by the cumulative effect of the n pulses, and is stopped by a pulse from another train of pulses out of phase with the first train. The train of short impulses D, Fig. 1, is applied to terminal 13, Fig. 3, and the out-of-phase impulses E, Fig. 1, to terminals 30, 33. The pulses at 13 pass through diode 15 and charge condenser 17 and deflector plate 11 cumulatively, thus deflecting the cathode-ray until after a predetermined number of pulses, say five, the beam reaches the collector plate 23, thereby initiating the output of the tube and causing current to flow through resistances 25, 26. The potential across 26 when added to the impulse E applied at 30, 33 breaks down the valve 28, thereby discharging condenser 17 and returning the beam to its normal position. Every fifth impulse of train D is thus repeated in the output circuit of the tube and these derived impulses may be applied to a further tube which repeats, say, the ninth derived impulse (i.e. the 45th impulse of train D) to a further tube and so on. The cathode-ray tube mav be constructed as described in Specification 366,053. Figs. 1 and 2 show the application of such a system for producing controlling and synchronizing impulses for a fourfold interlace having a total of 805 lines per picture, the line impulses falling from 30 to 15 per cent. of the carrier amplitude and the frame impulses falling from 30 per cent. to substantially zero. Pulse trains A, B, Fig. 1, at the line frequency and pulse trains C, D, E, F at four times the line frequency are first obtained by frequency multiplication from a tuning-fork generator or the mains. The out-of-phase trains C. D,E, F may be obtained by sweeping a cathode-ray circularly over four target plates. The pulses D are applied to an electronic reduction stage 1, in which they accumulate in a deflecting circuit until the seventh brings a cathode-ray on a plate s. The ray is returned to normal by the next impulse E. Nine impulses S, thus derived, bring the ray of a stage 2 on the plate t until discharged by the next pulse C. Twelve derived impulses T bring the ray of a stage 3 on a plate u at the 756th D-pulse, i.e. atthe 189th line which is the last picture line in the first frame. The derived impulses U cause a circuit 9 to bring the carrier to black level, release a blocking circuit 10 so that the pulses C reach a stage 4, cause a circuit 11 after two D-pulse periods to block the pulses S which would reach the stage 2, and release a blocking circuit 12 after three D-pulse periods so that the pulses S reach stages 6, 7, 8. The stage 4 is operated by six pulses C and discharged by the next pulse D and the stage 5 is operated by eight derived pulses V to produce a pulse W after 804 D-impulses, i.e. just before the end of a complete frame period. The next pulse S but one after a pulse U brings the ray of the stage 6 on a plate x so large that the ray remains on it for two more S pulses and produces a pulse X, which brings the carrier to zero for a framing signal, and releases a blocking circuit. 13 to allow the pulses F to inject line pulses in the framing pulse. The last pulse S brings the beam of the stage 7 on a large plate y to produce a pulse Y which discharges the stage 6 to complete the framing signal and again blocks the pulses F. At the end of the framing period the S pulses bring the beam of the stage 8 on a plate z to discharge the stage 7. Just before this, the pulse W from the stage 5 has (1) discharged the stage 3 to disconnect the black-level circuit 9, (2) released, after two D-pulse periods, the blocking circuit 11, and (3) restored the blocking circuits 10, 12.